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Biomedical subjects

P D Thompson

Publications and source records attributed to P D Thompson.

At least 145 records · Page 8Linked to original sources
PubMed1994

The auditory startle response in progressive supranuclear palsy.

The EMG characteristics of the normal auditory startle response in man are compatible with an origin in the pontine reticular formation and with conduction down the spinal cord in a slowly conducting, possibly reticulo-spinal pathway. The startle was reduced or absent in patients with progressive supranuclear palsy, consistent with loss of neurones in the lower pontine reticular formation. In contrast, the startle was present and of normal form in patients with Parkinson's disease. However, it was delayed in onset. This result was not influenced by treatment with L-dopa. The late auditory startle in Parkinson's disease might be related to withdrawal of facilitatory input to brainstem centres from the basal ganglia.

Aged↗
PubMed1994

Cortical reflex myoclonus in patients with the mitochondrial DNA transfer RNA(Lys)(8344) (MERRF) mutation.

Five patients from three families with the syndrome of myoclonic epilepsy and ragged red fibres (MERRF), associated with the mitochondrial DNA point mutation at position 8344, were studied neurophysiologically to determine the characteristics of their myoclonus. The findings were those of cortical reflex myoclonus, with enlarged cortical somatosensory evoked potentials and late reflex responses to peripheral nerve stimulation. Electroencephalography showed paroxysmal spike and polyspike and wave discharges, with photic sensitivity. This pattern of electrophysiological abnormalities was uniform, despite considerable variation in severity of myoclonus. Although a consistent finding, cortical reflex myoclonus is not specific to MERRF amongst myoclonic syndromes.

Adult↗
PubMed1994

Lipoprotein lipase activity and plasma triglyceride clearance are elevated in endurance-trained women.

Numerous studies have examined factors regulating high-density lipoprotein cholesterol (HDL-C) levels in male endurance athletes, but few studies have examined HDL-C regulation in female athletes. The present study compared lipid and lipoprotein concentrations, postheparin lipolytic activities, and the clearance rate (K2) of triglycerides following an intravenous fat infusion in 12 female distance runners (aged 33 +/- 9 years, mean +/- SD) and 13 sedentary women (33 +/- 9 years). Runners were leaner and had greater maximum oxygen uptake values than controls. Runners also had nonsignificantly lower triglyceride (53 +/- 15 v 65 +/- 13 mg/dL) and higher HDL-C (62 +/- 14 v 52 +/- 8 mg/dL, P = .06). Lipoprotein lipase activity (LPLA) was 33% greater (P < .05) and fat clearance (K2) was 27% faster (P < .01) in the trained women, and LPLA correlated directly with K2 (r = .61) and HDL-C (r = .62) in this group (P < .05 for both). K2 was directly related to HDL-C in the athletes (r = .57, P = .06), and also when the active and sedentary women were combined (r = .43, P < .05). These results suggest that increased LPLA and enhanced plasma triglyceride clearance may contribute to the HDL-C levels of physically active premenopausal women.

Adult↗
PubMed1994

The effect of magnetic coil orientation on the latency of surface EMG and single motor unit responses in the first dorsal interosseous muscle.

We examined the effect of the orientation of a figure-of-eight coil on the latency of surface electromyographic (EMG) responses and the firing pattern of single motor units evoked in the first dorsal interosseous muscle by transcranial magnetic brain stimulation. Two coil positions were used: the coil held on a parasagittal line either with the induced current in the brain flowing in a postero-anterior direction (PA) or with the current flowing latero-medially (LM). The results were compared with those observed after anodal electrical stimulation. LM stimulation produced surface and single unit responses which occurred 0-3 msec earlier than PA stimulation. In many cases responses to LM stimulation had the same latency as those produced by anodal electrical stimulation. Responses evoked by LM stimulation were less affected by changes in motor cortical excitability (cortico-cortical inhibition and transcallosal inhibition) than those to PA stimulation. We suggest that LM stimulation can sometimes stimulate corticospinal fibres directly, at or near the same site as anodal stimulation. In contrast, PA stimulation tends to activate corticospinal fibres trans-synaptically. The difference in stimulation sites may make a comparison of PA and LM stimulation a useful method of localising changes in corticospinal excitability to a cortical level.

Adult↗
PubMed1994

Rapid wrist movements in patients with essential tremor. The critical role of the second agonist burst.

Ballistic wrist flexion movements towards 15, 30 and 60 degrees visual targets were studied in a group of 17 patients with hereditary essential tremor. Compared with age-matched normal subjects (n = 16), there were three main kinematic differences: patients overshot the target a little more; the kinematic profile of their movements was more 'asymmetric' due to higher peak decelerations; and their movements initiated tremor. Ballistic movements performed by patients with essential tremor were associated with a triphasic pattern of agonist-antagonist-agonist muscle activity similar to that of normal subjects. The duration and size of each EMG burst was normal. The onset latency of the antagonist EMG burst was also normal, but the onset of the second agonist EMG burst was delayed. The delay in the onset of the second agonist EMG activity resulted in unopposed action of the antagonist muscle in the second half of each movement. As a result, deceleration occurred too rapidly as the hand returned past the target leading to a series of damped oscillations around the point of aim. The onset latency of the second agonist EMG burst correlated significantly with the tremor period; the longer the period the later the burst. We speculate that the delay in the second agonist burst reflects an abnormality in the timing of anticipatory muscle activity in essential tremor and that this may involve cerebellar mechanisms.

Adult↗
PubMed1994

A study of hereditary essential tremor.

Twenty index patients with hereditary essential tremor and their kindreds were studied to define the phenotype of this condition. Ninety-three first degree and 38 more distant relatives were examined; 53 definite and 18 possible secondary cases were identified. The age of tremor onset was bimodally distributed with a median at approximately 15 years. Segregation analysis indicated autosomal dominant inheritance and penetrance was virtually complete by the age of 65 years. There were no examples of the disease skipping a generation. Men and women were affected in equal proportions. About 50% of cases were alcohol responsive. In the majority of families alcohol responsiveness was either consistently present or did not occur, but in 20% of kindreds definite heterogeneity of responsiveness was encountered within each family. The typical phenotype was a mild symmetrical postural tremor of the upper limbs. Tremor of the legs, head, facial muscles, voice, jaw and tongue occurred but never in isolation and rest, task specific (e.g. primary writing tremor) and primary orthostatic tremors were not found. Head tremor was invariably mild and 75% was of a 'no-no' type. Dystonia (e.g. torticollis and writer's cramp) were not encountered, a finding which strongly suggests that many previous studies of 'essential tremor' were contaminated by cases of idiopathic or hereditary torsion dystonia. No association with Parkinson's disease was found but classical migraine occurred in approximately 26% of cases and co-segregated with tremor. The severity of arm tremor (assessed using a clinical rating scale and by scoring tremor in Archimedes spirals) and disability increased with advancing age and increasing tremor duration, but there was no correlation between age at tremor onset and either tremor severity or disability. Men and women were affected with equal severity. The sex of the affected parent had no influence on the severity of tremor or the degree of disability experienced by an affected child. Disability commenced in the second decade and progressively increased. All the index patients and 59% of the definite secondary cases had tremor induced disabilities. Eighty-five percent of index patients and 38% of secondary cases also reported some degree of social handicap. Twenty-five percent of index patients and 12% of secondary cases had been compelled to change jobs or retire. Biological fitness was normal.

Adolescent↗
PubMed1994

Corticobasal degeneration. A clinical study of 36 cases.

The presenting features and their subsequent evolution in 36 patients with pathologically proven or clinically probable corticobasal degeneration are described. The most common initial complaint was of a unilateral 'clumsy, stiff or jerky arm' (n = 20). Typically the arm was akinetic, rigid and apraxic. In about a third of these the arm was held in a striking and characteristic fixed dystonic posture. Jerking of the arm, due to action and stimulus-sensitive myoclonus accompanied these symptoms in about a third of the cases. The next most common presentation (n = 10) was difficulty walking due to clumsiness and loss of fine motor control of one leg due to apraxia or dysequilibrium, or a combination of both. Sensory symptoms in the affected arm heralded the onset of illness in three and accompanied a motor disturbance in two cases. Presentation with dysarthria or a behavioural syndrome were rare. The symptoms progressed slowly, usually involving first the ipsilateral arm and leg, but gradually spread to affect all four limbs. After a mean follow-up of 5.2 years (range 2-8 years) gait difficulties and a supranuclear ophthalmoplegia had emerged in most patients and dysarthria and pyramidal signs were common. Higher mental function was relatively preserved in most and a cortical sensory loss was evident in a quarter of cases.

Adult↗
PubMed1994

The myoclonus in corticobasal degeneration. Evidence for two forms of cortical reflex myoclonus.

The clinical and physiological characteristics of myoclonus in 14 patients with corticobasal degeneration are described. The myoclonus was focal, confined to one limb (usually the arm) and was most prominent on voluntary action or in response to sensory stimulation. On clinical inspection, the myoclonus appeared to occur at rest but EMG recordings revealed that apparently spontaneous myoclonus occurred only on a background of more or less continuous muscle activity (responsible for the rigidity and dystonia). The jerks consisted of hypersynchronous short duration bursts of EMG activity coincident in agonists and antagonists. Reflex myoclonus in hand muscles, to stimulation of the median nerve at the wrist, had a latency of approximately 40 ms. In 13 of the 14 patients reflex myoclonus was not associated with enlargement of the cortical sensory evoked potentials (SEPs); the later components of the parietal SEP were poorly formed and dominated by a broad positive wave with a peak latency approximately 45 ms. Prefrontal components of the SEP were relatively preserved, but there were no significant differences between the SEPs evoked from myoclonic and non-myoclonic limbs. Action myoclonus was not preceded by an identifiable cortical wave in the electroencephalogram back-averaged before each jerk. Magnetic, but not electric, brain stimulation evoked repetitive bursts of myoclonus suggesting enhanced cortical excitability. The combination of focal, predominantly distal, hypersynchronous jerks, evidence of enhanced cortical excitability, together with the known cortical pathology in corticobasal degeneration suggests that the myoclonus in these patients may be cortical in origin. Since the latency of reflex myoclonus in corticobasal degeneration is only 1-2 ms longer than the sum of the afferent and efferent times to and from the cortex, we propose the reflex myoclonus is mediated by direct sensory input to motor cortical areas that activate corticospinal tract output. Such myoclonus differs from the typical form of cortical reflex myoclonus in which reflex jerks have a longer latency (50 ms in hand muscles), cortical SEPs are enlarged and action myoclonus is preceded by a cortical discharge. It is proposed that these various forms of cortical myoclonus can be explained by the presence of different cortical relays of sensory information to cortical motor areas. The myoclonus of corticobasal degeneration may represent enhancement of a direct sensory input to the motor cortex. In contrast, the more widely recognized variety of cortical reflex myoclonus may involve abnormal relays through sensory cortex to motor cortex, either directly or via cerebellar-thalamo-cortical projections.

Adult↗
PubMed1994

Pathophysiology of hemimasticatory spasm.

Two patients aged 21 and 50 years presented with facial hemiatrophy and unilateral spasms of the masticatory muscles. Masticatory muscle biopsy showed normal findings in both patients and facial skin biopsy specimens only showed atrophy, although morphoea (localised facial scleroderma) had been diagnosed nine years previously in the second patient. The involuntary movements consisted of brief twitches and prolonged contractions clinically and electromyographically similar to those of hemifacial spasm and cramps. The jaw jerk and the silent periods were absent in the affected muscles. Direct stimulation of the muscle nerve and transcranial stimulation of the trigeminal root demonstrated slowing of conduction and after-activity due to autoexcitation. Observations in other reported cases and these two patients suggest that hemimasticatory spasm is produced by ectopic activity secondary to focal demyelination of the trigeminal motor nerve fibres. The proposed cause of the neuropathy is focal damage to the masticatory nerves caused by compression, possibly resulting from the deep tissue changes that occur in facial hemiatrophy.

Adolescent↗
PubMed1994

Dystonia after head trauma.

Dystonia is a rare consequence of head trauma. We describe 10 such cases and review 19 similar patients reported in the literature. Twenty-two of the 29 patients suffered head injury during the first or second decade of life. There was a variable delay between the head trauma and the onset of dystonia. In 18 cases with severe head injury, this interval (median, 18 months; range, 1 month to 9 years) was longer than in 11 cases with mild head injury (median, 14 days; range, 3 days to 5 years). In our series, nine of the 10 cases started as a focal dystonia and one as a hemidystonia. The dystonia progressed and spread over several months or years. Two cases remained as focal dystonias, but the others developed segmental, hemi-, multifocal, or generalized dystonia. On brain imaging studies (CT or MRI), the most frequent lesion site was in the contralateral basal ganglia or thalamus, but two cases had normal brain scans. Dysfunction of the lenticulothalamic neuronal circuit seems to be related to the development of dystonia following head trauma.

Adolescent↗
PubMed1994

Renal allograft preservation: a comparison of University of Wisconsin solution and of hypothermic continuous pulsatile perfusion.

A study was performed to compare early allograft function in kidneys preserved with University of Wisconsin (UW) solution to kidneys preserved by hypothermic pulsatile perfusion. The study consisted of two sets of data. The first set was a donor-paired study (matched data) of 30 heart-beating, hemodynamically stable donors. After removal from the donor each cooled kidney was individually prepared for preservation. One kidney was flushed with +/- 500 ml of UW solution and stored in UW solution on slushed ice. The other kidney was continuously perfused with cooled (4-6 degrees C) cryoprecipitated plasma. The kidneys were transplanted into suitable recipients in a random sequence. Twelve donors were excluded from the study because one or both kidneys were transplanted into recipients who had previously been transplanted. The remaining 36 kidneys were implanted into two similar groups after a mean of 19 hours in the pulsatile perfusion group and 18 hours in the UW solution group. The second set of data consisted of all the kidneys preserved in UW solution (n = 62) at our institution and of 57 kidneys preserved by hypothermic continuous pulsatile perfusion during the same period (mixed data) and was used to evaluate the effect of prolonged preservation (longer than 24 hours) on delayed graft function. Both of these groups were also comparable. Acute tubular necrosis (ATN) was defined as the need for dialysis during the 1st week after transplantation, and delayed function as the delayed clearance of creatinine during the early post-operative phase.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine↗
PubMed1993

Modulation of postural wrist tremors by magnetic stimulation of the motor cortex in patients with Parkinson's disease or essential tremor and in normal subjects mimicking tremor.

The effect of magnetic brain stimulation on postural wrist tremor was studied in 10 patients with Parkinson's disease, 12 with hereditary essential tremor, and 10 normal subjects who mimicked tremor by making rapid alternating wrist movements. In all patients and normal subjects, magnetic brain stimulation over the contralateral motor cortex at an intensity approximately 10% above threshold produced the following sequence of events: (1) a small direct electromyographic (EMG) response, followed by (2) suppression of the rhythmic EMG activity responsible for the tremor, before (3) reappearance of the tremor time-locked to the stimulus. It is concluded that magnetic brain stimulation over the motor cortex can modulate the oscillatory mechanisms responsible for the generation of postural tremors. Group analysis revealed that the time to reappearance of rhythmic EMG activity varied significantly with the period of parkinsonian postural tremors, but not with the period of essential or mimicked tremors. Magnetic stimulation also significantly shortened the period of parkinsonian postural tremors, but did not influence the period of essential or mimicked tremors. These behavioral differences indicate differences in the pathophysiological mechanisms underlying parkinsonian postural tremor and essential tremor.

Adult↗
PubMed1993

A positron emission tomography study of essential tremor: evidence for overactivity of cerebellar connections.

The origin of essential tremor is unknown. Animal models have suggested that the inferior olivary nucleus may act as a tremor generator. We used positron emission tomography to study changes in regional cerebral blood flow associated with involuntary postural tremor and passive wrist oscillation in patients with essential tremor. Activation due to voluntary wrist oscillation and arm extension without tremor was studied in normal control subjects. The essential tremor group had bilaterally increased cerebellar blood flow at rest (without tremor) compared with the control group. Involuntary postural tremor was associated with further bilateral cerebellar activation, and also contralateral striatal, thalamic, and sensorimotor cortex activation. Voluntary wrist oscillation, maintained arm extension without tremor, and passive wrist oscillation were all associated with significant ipsilateral rather than bilateral cerebellar activation. We conclude that essential tremor is associated with increased bilateral cerebellar activity both at rest and during tremor.

Adult↗
PubMed1993

Effectiveness of piracetam in cortical myoclonus.

Twenty-one patients with disabling spontaneous, reflex, or action myoclonus due to various causes, who had shown apparent clinical improvement on introduction of piracetam, entered a placebo-controlled double-blind crossover trial of piracetam (2.4-16.8 g daily). All but one patient had electrophysiological evidence of cortical myoclonus. Patients were randomly allocated to a 14-day course of piracetam followed by identical placebo, or placebo followed by piracetam. Nineteen patients received piracetam/placebo in addition to their routine antimyoclonic treatment (carbamazepine, clonazepam, phenytoin, primidone, sodium valproate, or tryptophan plus isocarboxazid, alone or in combination) and two received piracetam/placebo as monotherapy. All patients were rated at the end of each treatment phase using stimulus sensitivity, motor, writing, functional disability, global assessment, and visual analogue scales. Ten of the 21 patients had to be rescued from the placebo phase of the trial because of a severe and intolerable exacerbation of their myoclonus. No patients required rescue from the piracetam phase of the double-blind trial. When the 21 patients were considered together, there was a significant improvement in motor, writing, functional disability, global assessment, and visual analogue scores during treatment with piracetam compared with placebo. The total rating score also improved significantly with piracetam, by a median of 22%. Piracetam, usually in combination with other antimyoclonic drugs, is a useful treatment for myoclonus of cortical origin.

Adult↗